A secret society is a social organization that requires its members to conceal certain activities—such as rites of initiation or club ceremonies—from outsiders. Members may be required to conceal or deny their membership, and are often sworn to hold the society's secrets by an oath. The term "secret society" is often used to describe fraternal organizations (e.g. Freemasonry) that may have secret ceremonies, but is also commonly applied to organizations ranging from the common and innocuous (collegiate fraternities) to mythical organizations described in conspiracy theories as immensely powerful, with self-serving financial or political agendas, global reach, and often satanic beliefs.

Historically, secret societies are often the subject of suspicion and speculation from non-members, and as such have aroused nervousness from outsiders since at least the time of the ancient Greeks. For this reason, secret societies are illegal in several countries. In the European Union, Poland has made the ban a part of its constitution. Article 13 of the Constitution of the Republic of Poland states:

"Political parties and other organizations whose programmes are based upon totalitarian methods and the modes of activity of nazism, fascism and communism, as well as those whose programmes or activities sanction racial or national hatred, the application of violence for the purpose of obtaining power or to influence the State policy, or provide for the secrecy of their own structure or membership, shall be prohibited."

Some secret organizations exploit secrecy as a means to further political or criminal agendas, including such historical examples as the Know Nothing party in the United States, and the Mafia, respectively.

Many student societies established on university campuses [1] have been considered secret societies. The first collegiate secret society was the Flat Hat Club (1750), followed by Phi Beta Kappa (1776), both founded at William & Mary. The most famous member of the FHC was Thomas Jefferson, the third President of the United States. In correspondence, Jefferson noted that the Flat Hat Club served "no useful object." Some famous secret societies include the Skull and Bones (1832) at Yale University, the Order of the Bull's Blood (1834) at Rutgers University and the Bishop James Madison Society (1812) at The College of William & Mary.

List of Secret Societies

Business, International or Non-Governmental Organizations

While not self-styled as secret societies, these groups qualify through a quantative denotative interpretation.

• Bilderberg Group
• Club of Rome
• Council on Foreign Relations
• Royal Institute of International Affairs (also known as Chatham House)
• Society of the Elect
• Round table groups
• Trilateral Commission

Student Societies

• ANGRA at City University, London
• ANAK at the Georgia Institute of Technology
• Basiliaz at Northwestern University
• Berzelius (1848) at Yale University
• Bishop James Madison Society (1812) at the College of William and Mary
• Book and Snake (1863) at Yale University
• Brotherhood of the Golden Dagger (1895) at Rutgers University, inactive as of 1948
• Bullingdon Club at the University of Oxford
• Cambridge Apostles (1820) at the University of Cambridge
• Capitolo Otto at Yale University
• The Conscience at Oxford College of Emory University
• Episkopon at the University of Trinity College
• Flat Hat Club (1750) at the College of William and Mary
• L.O.S.A.B. at the University of St Andrews
• Michigamua (1902) at the University of Michigan
• Mountain at West Virginia University
• NoZe Brotherhood at Baylor University
• Order of the Bull's Blood (1834) at Rutgers University
• Owl Society at the University of Pennsylvania
• Phi Beta Kappa (1776) at the College of William and Mary, began as a secret society, but eliminated secrecy in 1831 and is now national
• Porcellian Club (1791) at Harvard University
• Prophets of Providence at Culver Military Academy
• Quill and Dagger (1893) at Cornell University
• Scroll and Key (1842) at Yale University
• Seven Society at the University of Virginia
• Shifters (1932) at Wittenberg University
• Skull and Bones (1832) at Yale University
• Society of the Pacifica House (1823) at Brown University
• Sphinx Head Society (1890) at Cornell University
• Sword and Serpent (1870) at Rutgers University
• Tabard at the University of Pennsylvania
• Theos at the University of Pennsylvania
• The Machine (1914) at the University of Alabama
• Wizards at Wittenberg University
• Wolf's Head (1883) at Yale University
• Z Society (1892) at the University of Virginia

Fraternal Organizations

• AMORC (Ancient Mystical Order Rosae Crucis)
• Confraternity of the Rose Cross
• Freemasonry (also known as Free & Accepted Masons)
• FUDOFSI
• FUDOSI
• Hekal Tiamat
• National Society of Pershing Rifles
• Order Militia Crucifera Evangelica
• Order of DeMolay
• Order of the Eastern Star
• Order of the Solar Temple
• Ordo Templi Orientis
• Perfect Masons
• Rosicrucians

Criminal Organizations

• Camorra
• Mafia (also known as La Cosa Nostra)
• Tong
• Triad
• Yakuza

Historical Secret Societies

• Black Panthers
• Illuminati
• Know-Nothings
• Ku Klux Klan
• Wide Awakes
• SPK

Revolutionary or Underground Organizations

• Carbonari
• Fenian Brotherhood
• Germanenorden
• Mau Mau
• Narodnik
• Society of Harmonious Fists
• Vihan Veljet
• Muslim Brotherhood

Alleged secret societies

• Bostonian Adventure Society
• The Elders of Zion
• Priory of Sion

In Works of Fiction and Popular Culture

• Aes Sedai Ajahs in Robert Jordan's The Wheel of Time, particularly the Black Ajah
• Angelic Society
• Brotherhood of the Cruciform Sword in Indiana Jones and the Last Crusade.
• Cabal, in the works of Robert A. Heinlein
• Central Anarchist Council in G.K. Chesterton's The Man Who Was Thursday
• Committee to Unelect the Patrician in Discworld
• Darkfriends, in Robert Jordan's The Wheel of Time
• Elucidated Brethren of the Ebon Night in Discworld
• House of Flying Daggers (in the movie of the same name)
• Illuminati in Tomb Raider (movie)
• Kom'Roya
• The League of Extraordinary Gentlemen
• Les Soldats in Noir
• Majestic_12 in the PC game Deus Ex by developer Ion Storm Inc.
• Millennium Group in the television show Millennium
• The Patriots in the Metal Gear video game series
• S.P.E.C.T.R.E., in the works of Ian Fleming
• Order of the Phoenix, in J.K. Rowling's Harry Potter series
• The Stonecutters, from The Simpsons
• Second Foundation, in The Foundation Series by Isaac Asimov
• Sisters of the Dark in the Sword of Truth series by Terry Goodkind
• The Trust , in the Vertigo/DC comics series 100 Bullets
• In the Mike Myers film So I Married an Axe Murderer, a character speaks of a secret organization called the Pentaverate , consisting of "the Queen, the Vatican, the Gettys , the Rothschilds and Colonel Sanders," which controls everything in the world, including the newspapers, and meets triannually at a secret location in Colorado called The Meadows.